Anti-microbial resistance among human bacterial pathogens is growing at an alarming rate and threatens the effectiveness of antibiotics. Resistant infections are associated with higher morbidity, mortality, and healthcare costs than infection with susceptible organisms. It is important to formulate a simple but robust method for estimating the cost of resistance that can be used by policy makers at all levels of the healthcare system. This proposal uses utilization rather than cost as our main outcome measure for estimation, inference, and guiding cost model development. Utilization reflects care actually rendered and provides common ground for cost estimation by users with different concepts of cost. We plan to construct a utilization profile comprised of individual elements such as length-of-stay ant procedures. We will also collect indirect costs, such as days lost from work, through case interviews. Because Staphylococcus aureus (SA) is one of the most important bacterial causes of human infectious disease morbidity and mortality and is a classic example of the successful adaptation of a pathogen to widespread antibiotic use, we will develop our model using SA infections. In order to make the model generalizable, it is necessary to have a complete picture of SA disease and not limit it to adult inpatient infection. We will study healthcare; and community-associated SA disease encompassing invasive and non-invasive cases. We will use prospective and retrospective data from heterogeneous sources and capitalize on our ongoing surveillance systems. Differences in utilization profiles of resistant and susceptible SA will be analyzed using multivariate statistical analysis due to expected high correlations among utilization components. This will make the method more sensitive to detection and estimation of differences. The results of statistical analysis will be used to inform the development and selection of a single "best" cost model that will be implemented in a spreadsheet tool. This tool can be adapted to the perspectives of different decision makers including healthcare providers, healthplan and hospital administrators, government, and others. The output of the cost model will feed the input of a more general societal economic model that will incorporate community transmission and costs associated with spread of MRSA to others in the community. This is the first time a society-wide estimate of the cost of resistance has been attempted.